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MOZ
MOZ

Posted: Mon May 04, 2015 7:54pm

Post Subject: Domestic Electrical Equipment

Is there a simple formula for working out what electrical appliances can be used on a boat with inverter fitted.

Tony-B
Tony-B

Posted: Mon May 04, 2015 8:49pm

Post Subject: Domestic Electrical Equipment

Simple answer â NO. This is because there are two different types of inverter, two ways of expressing their output and then something known as power factors to be taken into account. I will ignore power factors but if the inverter output is only a little above the power rating for your equipment then it may not work. You also have to bear in mind that things like motors produce a significant starting surge so again a marginal inverter size may not work. Then there is a question about how suitable your battery capacity, state of charge and wiring is to supply an inverter. Running a kW inverter at full power on 2 x 110Ah domestic batteries is a recipe for battery disaster. Inverters come in two basic types: MSW, modified sine wave that are usually cheaper and PSW, pure sine wave. The PSW inverter should run anything within its power rating but MSW ones can destroy equipment, cause overheating and noisy operation, interference on some audio-visual equipment and things with electronic control like microwaves and washing machines may simply refuse to work. Each inverter should have two output ratings, the maximum or peak one we will ignore and hope that it is enough to cope with cover starting surges. Work with the continuous one. Letâs say you have a 1.5 kW continuous inverter. You need to convert this to Watts and Amps because the rating plate on the back of your appliances may quote either unit. 1kW = 1000 Watts so 1.5 kW = 1500 Watts. Amps = watts divided by voltage so 1500/240 volts = 6.25 amps. So now you know that if the sum of the consumption (from the plate at the back) all the equipment you run at any one time is less than 1500 watts or 6.25 amps in most cases it should run. However be aware of the complications caused by the power factor and starting surge. You may wish to over-specify the inverter to be on the safe side. To get an idea if the battery bank can cope take the Watt rating and divide in by 10 or the 240 volt Amps rating and multiply it by about 20. That will give you the current the inverter will take from the batteries. My first example of a 3kW inverter on a 220 Ah battery bank gives a current draw of 3000/10 = 300 amps so in theory you could run it from a fully charged 220 Ah bank for 220/300 = 0.73 of an hour. In practice the bank is unlikely to be fully charged and the inverter should cut out at a certain point to protect the batteries so that figure is totally unreal. Think 20 minutes and then many. Many hours running to recharge the bank. Sorry this is so complicated but there really is no easy answer although some may allegedly give you one that works most of the time.

Tony-B
Tony-B

Posted: Tue May 05, 2015 9:17am

Post Subject: Domestic Electrical Equipment

PS, should have said that if you want more information it may be better to email Tony@TB-Training.co.uk (no line break and with the hyphen). That way I can break eh text up into paragraphs so it is easier to understand and also include diagram if needed.

MOZ
MOZ

Posted: Fri May 15, 2015 8:43pm

Post Subject: Domestic Electrical Equipment

Thank you Tony, I think that answers my query but I may be intouch later.

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